1. Field of The Invention
The invention relates to a stimulation system of the type wherein a stimulation unit is connected to skeletal muscle by implantable electrodes and controlled by a pacemaker.
2. Background Information
Severe therapy resistant cardiac insufficiency -- a significant problem because of its frequency of occurrence and mortality -- can be treated with the technology of cardiomyoplasty.
In cardiac surgery there is generally a great demand for systems which are able to fully or partially take over the heart's pumping function. Cardiomyoplasty -- this promising method which has been in clinical use since 1985 -- is a technique for functionally replacing the loss of cardiac muscle tissue by skeletal muscles, particularly by the latissimus dorsi muscle (LDM). Surgical interventions are known to have been performed in cardiac patients to support heart contractions by placing a striated skeletal muscle of the patient's own body, preferably from the area of his back, completely or partially around the heart.
It is also known that this skeletal muscle can be trained by chronic electrostimulation for six weeks with low frequencies around 2 to 10 Hz whereupon it becomes relatively resistant to fatigue. The conversion of the muscle tissue, which is composed originally of types of muscle fibers, is here effected in such a way that the more fatigue resistant type is in the majority at the end of conditioning.
Stimulation systems have been developed which emit individual pulses in short succession (burst stimulators). Since the skeletal latissimus dorsi muscle (LDM) stimulated by an individual pulse reacts with a contraction that last about 70 ms, but the time period of the systole of the heart lasts 200 to 250 ms, the muscle contraction is electronically adapted to the time curve of the heart contraction. The duration of the contraction is then extended to correspond to the burst duration. Such a known implantable pacemaker is constructed of two channels, with each channel including a receiving unit, a synchronizing unit and an output unit.
The drawback in the prior art system is the fact that the stimulation is always effected with constant values and is thus not adapted to the momentary physical stress.